As long as I work on one problem, I remember all methods I have written and what they do. I also keep the architecture in my head and the approach I have chosen

As long as I work on one problem, I remember all methods I have written and what they do. I also keep the architecture in my head and the approach I have chosen to solve the problem. This works fine as long as I am not interrupted. I cannot recommend trying to hold too much in your head at once. I has a bad effect on your creativity. Free your mind instead to have all necessary resources available to find the best solution for the current problem. It is also an achievement to break down large chunks of work into small parts and solve only the small parts. In this perspective it is absolutely useless to keep code in the head. It is written in the editor right in front of your eyes anyway.